<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>画三角形</title>
    <style>
        body{
            width: 100%;
            height: 100%;
            display: flex;
            justify-content: center;
            align-items: center;
        }
        .box {
            /* width: 100px;
            height: 100px; */
            /* background-color: yellow; */
            /* border-top: 50px solid transparent; */
            border-left: 50px solid transparent;
            border-bottom: 50px solid yellow;
            border-right: 50px solid transparent;
        }
    </style>
</head>

<body>
    <div class="box"></div>
</body>

<script>

</script>

</html>